This invention relates generally to a preformed gasket and, more specifically, to a resilient molded gasket adapted to be retained in a preformed groove.
The present invention is especially suitable for use with components such as spin-on oil filters having a preformed gasket secured in a groove to insure that an unused gasket is in place when the filter is installed. Spin-on filters are made with an open end adapted to thread onto a mounting adaptor and having either a rectangular, lathe-cut gasket or a molded gasket secured into a groove formed in the open end. The gasket is typically located near the outer periphery of the open end to establish a face seal between the filter and the mounting adaptor.
Conventional gaskets utilized in spin-on filters are lathe-cut gaskets made from a relatively hard rubber material. Lathe-cut gaskets are typically less expensive than molded gaskets, and the relatively high durometer of a lathe-cut gasket permits the gasket to be mechanically secured into a groove by forming intermittently-spaced staking tabs in the sidewalls of the groove. The staking tabs protrude into the gasket to grab and hold the gasket in the groove.
Staking a lathe-cut gasket is a relatively complicated and expensive process. The formation of the staking tabs must be held within relatively close tolerances to avoid damage to the gasket that would affect the ability of the gasket to establish a seal. In addition, the nature of the staking operation requires that the width of the groove be held to relatively close tolerances and be formed so that there is very little radial clearance between the gasket and the sidewalls of the groove. Despite these disadvantages, staking a lathe-cut gasket is generally preferred over the prior alternative procedures (discussed below) associated with mechanically securing molded gaskets in a groove.
Apart from the manufacturing considerations, the use of a lathe-cut gasket may cause difficulties during the installation and removal of a filter. Specifically, lathe-cut gaskets can result in the need to apply a relatively high tightening torque when the filter is seated against the mounting adaptor. The rectangular lathe-cut gasket presents a relatively large, flat sealing face for sealing to the sealing surface of the mounting adaptor, and this results in relatively high friction between the seal and the mounting adaptor. Staking also prevents the gasket from rotating with the groove. As a result, a substantial portion of the torque applied to seat the filter is absorbed by shear deformation of the gasket and by the friction between the gasket and the mounting adaptor. Additionally, the relative hardness of a lathe-cut gasket and the small radial clearance between the gasket and the groove make it difficult to compress the gasket.
During the time that the filter is installed, long-term exposure to heated oil may cause a lathe-cut gasket to permanently swell. As a result, the flat sealing surface of the lathe-cut gasket tends to "weld" to the sealing surface of the mounting adaptor and thus removal of the filter may require substantial more torque than did the installation of the filter.
Molded gaskets, on the other hand, offer advantages over lathe-cut gaskets with regard to the installation and removal of spin-on filters. Molded gaskets may be formed with rounded corners which permit the gasket to be more easily compressed. The rounded corners also avoid having a relatively large, flat sealing surface in initial contact with the sealing surface of the mounting adaptor. Additionally, since molded gaskets are more easily compressed, the radial clearance between the sidewalls of the groove and the gasket may be increased to permit the gasket to rotate more freely in the groove. As a result of the above factors, the torque required to install or remove a filter having a molded gasket is substantially less than the torque required to install or remove a filter having a lathe-cut gasket.
Prior molded gaskets are preformed with an L-shaped cross-section. The leg of the "L" typically extends radially inwardly from the body of the gasket and rests on the base of the groove. To secure the L-shaped gasket in the groove, a portion of the inner sidewall of the groove is turned approximately 90 degrees toward the outer sidewall, such portion being generally parallel with the base of the groove so as to trap the leg between the base and the deformed portion of the sidewall.
While prior L-shaped gaskets are axially retained in a groove without the need for a staking operation, an additional operation beyond simply inserting the gasket into the groove is required. In one procedure, the groove, including the turned-in portion of the inner sidewall, may be preformed and the gasket is installed into the preformed groove. In this instance, the gasket must be stretched so as to slip the inside periphery of the leg past the radially outward end portion of the turned-in sidewall. Alternately, the gasket may be installed into a groove having substantially parallel sidewalls. In such an instance, the inner sidewall is formed or rolled-over to capture the leg of the gasket in the groove. In either case, elimination of the staking operation requires substitution of another operation to retain the gasket in the groove.